Various sensing techniques have been suggested and employed for detecting incipient vehicle rollover including acceleration sensors operative on three axes, tilt sensors, level-gage and gravitation sensors. Micromechanical yaw and acceleration sensors are most commonly employed. Airbag triggering controls are adaptable for such sensing functions and are commonly utilized in rollover occupant protection systems to deploy, for example, extendable rollover bars and head airbags, and to trigger seat-belt tensioners.
Micromechanical yaw and acceleration sensors are also adaptable for use in rollover warning/mitigation controls which are intended to alert the operator of an incipient rollover or to take corrective actions to prevent the vehicle from turning over. Mitigation controls may utilizing various powertrain, steering, braking and suspension sub-systems. Generally, such warning/mitigation controls are influenced by the vehicle's lateral acceleration limits in accordance with the vehicle's characteristics which are determined by factors including center of gravity, track, mass, tire and road surface dynamics, etc.
The relative center of gravity height, i.e., the height of the center of gravity of the sprung mass relative to the roll center, has been shown to be a critical parameter in vehicle roll motion. Nominal values for a vehicle's relative center of gravity height can be readily determined. However, the actual relative center of gravity deviates from nominal in static and dynamic ways. For example, vehicle loading conditions generally effect a static change in the relative center of gravity. Static changes may be particularly acute in sport utility vehicle, trucks and vans. And, when a vehicle exhibits roll, the roll center of the sprung mass moves. Such motion introduces a dynamic change in the relative center of gravity height.
Deviation of the actual relative center of gravity from nominal will influence the performance of rollover warning/mitigation controls based on nominal relative center of gravity. Therefore, it is desirable to adapt rollover mitigation controls to such deviations. Hence, determination of the actual relative center of gravity of a vehicle is desirable.